Steel Cylinder 'Cloaks' Sound Waves

In 2009, Discovery News Tech writer, Eric Bland, wrote about a DVD-sized lens designed to bend sound waves, such as those used for sonar or ultrasound. The technology could be used to cloak underwater objects like submarines, making them invisible to sonar.

But in 2009, the technology was still in the conceptual stages. Now the researchers, lead by Nicholas Fang of the University Illinois, have produced an experiment that shows that their prototype works. They published their results in the journal Physical Review Letters. It’s also available HERE for download.

The disk is made from a metamaterial, a specially engineered material that has enhanced properties. In this case, the material is engineered to have 16 concentric rings that guide sound waves and bend them around outer layers of the cloak. This means that if something is inside the cloak, the sound waves will bend around it, too.

To test this, Fang and his team submerged the cloaking device in a tank of water and put a steel object inside it. On one side of the tank, they placed an ultrasound source and on the other side the placed a sensor array. When the steel object was inside the cloaking device, it didn’t show up on the ultrasound.

Their next experiments will look at various military applications for the technology as well as soundproofing and even health care.

Caption: Each ring on the cloaking device has a different index of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones. | Photo: L. Brian Stauffer